In recent years there has been a mounting demand for measurement of the room temperature distribution to detect the presence of human beings and their motion in a room in connection with security maintenance and air conditioning.
So far, there have been several methods that utilize infrared radiation in measuring the temperature distribution in an empty space, one being an application of two dimensional quantum effect type solid-state infrared image sensors and another being an application of pyroelectric infrared sensors.
In case of the quantum effect type sensors, a high accuracy in temperature measurement and a high resolution are achieved but the cooling system required by the sensors is too costly for their use with home appliances.
With regard to the method of using pyroelectric sensors in measuring the space temperature distribution, there is a method to find the temperature distribution by detecting the input energy of one direction after another through a single unit of a pyroelectric sensor that performs a directional scanning vertically as well as horizontally as disclosed in TOKUKAI-SHOW 64-88391, TOKUKAI-SHOW 57-185695, TOKUKAI-HEI 2-183752, TOKUKAI-HEI 2-196932, etc.
A pyroelectric sensor is capable of detecting infrared radiations and the thermal radiations in particular. It comprises two electrodes mounted on the both sides of a pyroelectric substrate which changes the electric potential across the two electrodes upon application of infrared radiations to it. For such a pyroelectric substrate, ferroelectric materials of glycine sulfate, polyvinylidene fluoride, LiTaO.sub.3, etc. are used as the raw materials. The ferroelectric materials of glycine sulfate, LiTaO.sub.3 and the like are used in a crystalline form and the one of PbTiO.sub.3 is used usually in the form of sintered ceramics or thin film prepared by a thin film technology since its crystallization is not easy.
The thin film sensor has high cost and reliability problems, but in contrast, the sensors of crystalline and ceramics have the features of excellent productivity and reliability. These crystalline or ceramic bodies are sliced and polished to thin plates to make sensor substrates. Over the outer surface of the substrates, electrodes are formed to complete an array sensor by having a series of sensor elements aligned on the substrates.
However, this array sensor had the problem of its output voltage changing sensitively against the temperature change and the vibration of the substrates.